Substation telephone circuits



T. G. MARTIN. SUBSTATION TELEPHONE CIRCUITS. APPLICATION FILED JAN. 21, 1921..

1 $24 368, Patented Aug. 11, 1922,

. mmzwm TALBOT G. MARTIN. CHICAGO, ILLINOIS, ASSIGNOR 'lO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

SUBSTATION TELEPHONE CIRCUITS.

Specification of Letters Eatent.

Patented Aug. 11, was.

Application filed January 21, 1921. Serial No. cancer.

To all whom it may concern:

Be it known that I, TALBOT G. MARTIN, a citizen of the United States of America, and a resident of Chicago, Cook County, and State of Illinois, have invented certain new and useful Improvements in Substation Telephone Circuits, of which the following is a specification. V

The present invention relates in general to substation telephone circuits, but more particularly to substation circuits for use in automatic telephone systems; and the'object of the invention, broadly stated, is to provide a novel and efl'ective circuit arrangement for introducing a well known type of calling device, or impulse sender, in a standard Bell common battery telephone circuit.

Calling devices have been associated with telephone circuits of this type before, and it has been the object of prior inventors along this line, to provide means for preventing clicks, or objectionable noises, in the telephone receiver when the impulse sender is being operated. it has also been considered necessary to shunt out the transmitter during the transmission of impulses, as the uncertain resistance of this member is apt to have a bad eil'ect on the impulses. To these ends it has been the practice to provide contact springs .for the impulse sender, which when the sender is moved from normal are effective to open the receiver circuit and to shunt the transmitter.

The main objects sought are thus accomplished, but the circuit arrangements used heretofore do not attain the desired results as efiiciently as possible. The principal trouble is in connection with the ringer circuit. it is desirable to bridge the ringer across the line without intervening switch hook contacts, as contacts for this purpose are not provided on the standard telephones, and it has been the practice heretofore to connect the ringer directly across the two line wires. This is not altogether satisfactory, for. the ringer is liable to tap the gongs during the transmission of impulses,-and in addition the bridged ringer and condenser are liable to injuriously affeet the quality of the transmitted impulses. It is the object of the present invention, considered more specificall to remove the defects pointed out, and e invention consists in an improvement or revision of the circuit arrangements whereb existing advantages are retained, while t efurther advantage of entirely eliminating theobjectiona ble ringer circuit diiiiculties is secured in simple and effective manner.

The improved circuits will now..,be described with reference to the accompanying drawings, in which Fig. 1 is a wiring diagram of the invention as applied to a wall telephone, while Fig. 2 is a simplified circuit diagram.

Referrin first to Fig. 2; the talking cirnormally open at the usual switch hook contacts, and are closed by the raising of the switch hook when the receiver is removed.

Associated with the lower side of the line is a subscribers impulse sender, which is indicated by the reference character S; This sender, or calling device, may be of thetype which is shown and described on pages 34 and 35 of Automatic Telephony by Smith and Campbell, published by the McGraw- Hill Book Company. Tt comprises essentially a pair of impulse sprin s 6 and 7.

which are controlled by a cam not shown) through the medium of a finger hold dial (also not shown), and three shunt springs 8, 9, and 10, together with suitable means for shifting spring 9 away from spring 10 and into engagement with spring 8 whenever the calling dial is turned from itsnormal'position. The impulse springs 6 and"? are connected in series with the lower line wire '3 and their function is to produce momentary interruptions of the line circuit for the purpose of operating the central ofiioe switches. The function of the set of springs 8, 9 and 10 is to provide for opening the receiver circuit and for shunting the transmitter when the calling device dial is being operated. In order to accomplish this object it will be seen that the receiver circuit is taken through normally closed contact springs 10 and 9, so that when these springs are separated by the operation of v by clicks or noises in his receiver.

Attention is now directed to the manner in which the ringer M is connected. One side of the ringer is connected to the upper line wire 2, while the other side of the ringer is connected to the condenser C, the other side of which is in turn connected to the lower side of the line at a point between the impulse spring 7 and the transmitter T. It will be seen then that since the impulse springs 6 and 7 are normally closed, the ringer and condenser C are for all practical purposes bridged directly across the line wires, at

least this is true so far as the reception of incoming ringing culrrents is concerned,

which are intended to operate the ringer and notify the subscriber that he is being called. But when the telephone is being used for an outgoing call and the impulsesender is being operated, the impulse springs 6 and 7 not only interrupt the usual direct current bridge across the line but they alsointerrupt the circuit of the bridged ringer. It follows that the line conductor 3 is entirely disconnected from the other line conductor every time the impulse springs are separated, and there is nothing bridged across the line at the substation which can in any way affect the quality of the impulses. Furthermore, since the ringer circuit is also interrupted by the impulse springs, the condenser C is not charged and discharged by the opening and closing of the impulse springs as would be the case if it was connected directly across the line conductors 2 and 3, and the ringer is thus prevented from tapping the gongs.

In Fig. 1 a specific form of the circuit shown in Fig. 2 has been drawn out in detail. The apparatus at the right comprising the transmitter T and the calling device S is intended to be mounted on the door of the telephone box; while the apparatus at the left, comprising the receiver R, switchhook H, ringer M, induction coil 1, and condenser C are mounted in the customary manner within the box itself. It will be seen that there are five conductors connectin the apparatus which is mounted on the oor with the other apparatus, and these conductors are preferably formed into a flexible cable in order to permit theopening and closing of the door. If desired, however, the door may be provided with a plurality of hinges,

through which the required connections are made. Suitable binding posts are provided in the base of the telephone box ior connecting the line wires and the receiver cord, and these binding posts are, of course, connected with the appropriate parts of the apparatus. A series of binding posts are also preferably provided on the inside of the door in order to facilitate the connection of the wires coming't'rom the transmitter and from the calling device.

The operation of the telephone substation embodying the new circuit is as follows: Referring to Fig. 2, when the receiver is removed to initiate a call, the switch hook lever H is permitted to rise and the previously described circuits of the transmitter and receiver are closed. Responsive to the closure of the transmitter circuit current is supplied to the transmitter from a bridged battery at the central oflice (not shown) over the following path: line conductor 2, winding 4 of the induction coil 1, right hand switchhook contact, transmitter T, and impulse springs 7 and (Ho line conductor 3. The bridge at the central office which includes the battery, may also, in accordance with the usual practice, include the controlling relay of an automatic switch, the circuit of such relay including, therefore, the transmitter bridge at the substation. It follows that the calling subscriber, by suitably manipulating his calling device dial, may produce a series of interruptions in the circuit of the controlling relay to bring about the operation of said switch.

It should be noted in this connection that when the dial is turned from its normal position, the substation loop is completed over a path which extends from the line conductor 2 by way of the winding 4 of the induction coil I, both contacts of the switchhook H, spring 9, spring 8 and the impulse springs 7 and 6 to the line wire 3. It will thus be seen that the variable resistance of the transmitter is excluded from the impulsing ciri cuit. Succeeding operations of the dial will now result in the operation of additional automatic switches at the exchange, until the connection is finally completed to the line of the called subscriber, it being understood that all the switches are provided with controlling relay bridges which, with the exception of the bridge in the last switch, are successively cut off from the line after their associated switches are operated.

The connection having been completed, conversation may be held as desired. Since the operation of the automatic circuits is well known it is not thought to be necessary to devote any space to the description of such operation herein. When the receiver is replaced at the end of the conversation the transmitter and receiver circuits are broken at the switch hook contacts and further flow of direct current through the subasagna V station fromthe exchange is prevented. As

a result all the switches at the central oiiice are released and restored to normalin' the usual and well known manner. The substation is now in condition to receive incoming signalling currents which may come in over the line conductors 2 and 3 and traverse the lid . transmitter and sai ringer M and the condenser C, whereby the ringer is actuated to advise the subscriber of an incoming call.

Having described m invention, what I consider to be new an desire tohave pro tected by Letters Patent will be pointed out in the appendedclaims.

Whatlclaimis:

1. In a substation circuit arrangement for telephone exchange systems, a" receiver, a transmitter, normall receiver, a switch for closin said circuits, an impulse sending device fiaving a definite normal position, meansfor moving said devicewout of its normal position, means for returningsaid device to its normal position, contacts operated during the last mentioned movement of saiddevice for sending impulses, a contact operated during said movementsof said device for opening the circuit of said re ceiver, another contact operated during said movements of said device for shunting said transmitter, a ringer, a condenser,and a ciropen circuits for said cuit for said ringer including said condenser and the said impulse sending contacts.

2. In a substation circuit arrangement for telephone exchange systems, a receiver, a transmitter, normally open circuits for said receiver and transm1tter,'means for closing said circuits, an impulse sending device, a pair of contact springs actuated by said device for transmitting impulses, means actu-v ated during the operation of said sending device for opening the receiver circuit and shunting the transmitter circuit, a ringer, a condenser, and a circuit for said ringer including said condenser and the said pair of contact springs.

3. In a telephone substation circuit, a receiver, a circuit therefor, a transmitter, a shunt. circuit therefor, an impulse sending device, contacts controlled by said device for transmittin impulses to the exchange, contacts control ed by said device for opening said receiver circuit and closing said shunt circuit whenever said device is moved from normal, a ringer and a circuit therefor including said first named contacts, and a condenser included in the ringer circuit and also in the receiver circuit.

Signed by me at Chicago, Cook County, Illinois, this 17th day of Jan. 1921.

TALBOT G. MARTIN. 

